Bacillus thuringiensis (B.t.) is a spore forming soil bacterium which is known for its ability to produce a parasporal crystal protein which is toxic to a wide variety of insects. Most strains are active against Lepidopteran insects (moths and butterflies) and a few are reported to have activity against Dipteran insects (mosquitoes and flies, see Aronson et al. 1986). Toxin genes from a variety of these strains have been cloned and the toxins have been expressed in heterologous hosts (Schnepf et al., 1981; Klier et al., 1982). In recent years, B.t. var. tenebrionis (B.t.t. , Krieg et al., 1983; Krieg et al., 1984) and B.t. var. san diego (B.t.sd., Herrnstadt et al., 1986) strains have been identified as having activity against Coleopteran insects. The toxin gene from B.t.sd. has been cloned, but the toxin produced in E. coil was reported to be a larger size than the toxin from B.t.sd. crystals, and activity of this recombinant B.t.sd. toxin was implied to be weak.
Insects susceptible to the action of the protein toxin of Coleopteran-type Bacillus thuringiensis bacteria include, but are not limited to, Colorado potato beetle (Leptinotarsa decemlineata), boll weevil (Anthonomus grandis), yellow mealworm (Tenebrio molitor), elm leaf beetle (Pyrrhalta luteola) and Southern corn rootworm (Diabrotica undecimpunctata howardi).
Therefore, the potential for genetically engineered plants which exhibit toxicity or tolerance toward Coleopteran insects was foreseen if such plants could be transformed to express a Coleopteran-type toxin at a insecticidally-effective level. Agronomically important crops which are affected by Coleopteran insects include alfalfa, cotton, maize, potato, rape (canola), rice, tobacco, tomato, sugar beet and sunflower.